In European patent document EP-A-0 439 754 there is described a power plant facility that has a gas-turbine group having waste-heat boiler and steam turbine ("GuD"=gas and steam turbine process). These processes today achieve electrical efficiencies of up to 58%.
A method of operating a gas turbine described in European patent document EP-B-0 650 554 discloses a mixed gas/steam turbine process in which the injected steam finds use for cooling the combustion chamber. By this means method, the combustion air is no longer required for cooling the combustion chamber, as in conventional gas turbines, but only for controlling the combustion process. For this reason, the ratio of compressor power to turbine power in such mixed gas/steam turbines can be markedly lower than in conventional gas turbines.
A further improvement in heat utilization can be achieved in this process by virtue of the fact that the waste heat of the mixed gas/steam turbine is also partly used for interheating of the steam-unit spent steam supplied to the combustion chamber.
In the processes described, a fact detrimental to the approach to the isothermal combustion power process is that the pressure level declines with the temperature upon the expansion of the working fluid, and so said approach is practically possible only with a few stages. As a consequence, however, substantial elements of the adiabatic combustion power process are preserved.